Higher cancer risk for marijuana smokers

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Researchers have found marijuana smoke contains a higher concentration of carcinogenic hydrocarbons than tobacco and also found that tetrahydrocannabinol (THC) - the major psycho-active component of marijuana - can promote tumour growth by impairing the body's immune system.

Reported in the July edition of the Journal of Immunology, the study was conducted by researchers from UCLA's Jonsson Cancer Centre, who found THC limited the immune response in mice, by increasing the availability of two forms of cytokine (IL-10 and TGF-beta), which are potent tumour-specific immunity suppressors.

"What we already know about marijuana smoke, coupled with our new finding that THC may encourage tumour growth, suggests regular use of marijuana may increase the risk of respiratory tract cancer" said head of the research team Dr Steven M Dubinett. Dr Dubinett said further studies would be needed to evaluate this possibility.

Whilst previous research has shown THC can lower resistance to both bacterial and viral infections, tumour-promoting activity has not before been reported.

In addition to impairing the body's immune system, the research also found the tar portion of marijuana smoke contains higher concentrations of carcinogenic hydrocarbons than tobacco smoke, including benzopyrene, a key factor in promoting human lung cancer.

Researchers also found marijuana smoke deposited four times as much tar in the respiratory tract as does a comparable amount of tobacco, thus increasing exposure to carcinogens.

The UCLA researchers examined the effects of THC on the immune response to lung cancer in mice.